There are various diagnostic methods for tumors, including clinical diagnosis, blood test and biochemical diagnosis, imaging diagnosis, pathological diagnosis, etc. Among them, pathological diagnosis is of key significance in identifying the benign and malignant nature of tumors. The reason why pathological diagnosis is called the “gold standard” of tumor diagnosis depends on the high dependence on pathological diagnosis in the process of tumor diagnosis and treatment. Pathologists analyze the abnormal changes of tumor cell morphology, tissue structure and growth pattern through microscopic observation, and detect the immunophenotypic characteristics of tumor cells and abnormal changes at molecular level through immunology, genetics and molecular biology to make differential diagnosis of tumor, including classification, typing, grading and naming of tumor, the invasive range of tumor, evaluation of the adequacy of surgical resection, whether the tumor is localized or metastasized to other organs, and evaluation of tumor invasion. The information is an important basis for clinicians to formulate and implement treatment plans. With the progressive understanding of molecular mechanism of tumor occurrence and development, more and more molecular targeted drugs are used in clinical treatment of tumors, and patients must apply molecular pathology testing technology for targeted molecular target detection before choosing targeted drug therapy. Pathological examination is also the “gold standard” of tumor treatment. Although pathological examination is a reliable method to confirm tumor diagnosis, there are certain limitations. For example, the pathologist does not have direct contact with the patient, and the relevant medical history, condition, symptoms and systemic examination can only be known through the textual content of the pathology application form, and the diagnostic features representing the essence of the lesion can only be identified through the complex phenomenon of the examination of the received tissue specimen, which requires the pathologist to have long-term rich experience in diagnostic practice. In addition, pathological diagnosis is also limited by the quality and quantity of specimens sent for examination, sometimes there are few tumor cells to make a correct diagnosis, and there are also tumor tissues with atypical morphology that are difficult to confirm the diagnosis. PET-CT may still be the best method for tumor review and recurrence. Generally speaking, tumor patients are required to have lifelong review and follow-up. The traditional methods of tumor review and follow-up include tumor marker examination, B-ultrasound, X-ray, CT MRI and so on. With the development of technology, PET-CT, one of the “three greatest medical inventions of the 20th century”, has shown its unique superiority. First of all, PET-CT can well distinguish the scar and tumor recurrence after surgery. Some traditional examinations, such as CT and MRI, mainly diagnose through the influence of tissue structure, such as tumor size, density, internal structure, relationship with surrounding tissues, etc. For tumor after surgery, because of the change of normal structure and the formation of surgical scar, conventional examinations are often difficult to compare with the scar. After tumor surgery, it is often difficult to distinguish from tumor recurrence because of the change of normal structure and the formation of surgical scar. However, PET-CT has not only structural image but also functional image, that is, through PET-CT, the metabolic situation of tissues can be seen, and there are obvious metabolic differences between post-operative scar and tumor recurrence. PET-CT is a single scan that can look at the whole body. Moreover, PET-CT is very sensitive to tumor metastases, whether they are metastases of other organs or lymph nodes, while conventional examinations are usually of one part of the body and need to be supplemented by other examination tests. The third trick: precise positioning Some conventional examinations are often unable to characterize and locate tumors, such as the elevation of tumor markers can only suggest the possibility of tumor recurrence, but cannot precisely locate recurrence and metastasis, while PET-CT can “characterize, locate, regularly and quantitatively”. PET-CT can diagnose the smallest tumor lesions with a size higher than that of conventional examination methods. Of course, PET-CT also has its disadvantages, and its high price is the reason why it is difficult to be popularized. Therefore, for patients with limited financial ability, PET-CT can be performed on the basis of abnormalities found in conventional examinations.